As is known in the art, an air brake system for a vehicle, typically includes an air chamber that, when the vehicle operator activates the brakes by pushing on the brake pedal, receives pressurized air to move a brake push rod that actuates a slack adjuster. As a result, a brake cam shaft is turned which causes the brake shoes of the system to engage brake drums at the wheels of the vehicle to slow or stop the vehicle. Over time, as the brakes are used, the brake push rod travel distance or stroke increases, eventually requiring readjustment of the brake system and/or replacement of components. As a result, various types of devices exist for monitoring the stroke of the brake push rod to provide a visual indication of an out of adjustment condition or excessive wear of vehicle brake components leading to brake failure.
An example of a prior art device for monitoring the stroke of a brake push rod is illustrated in U.S. Pat. No. 4,945,818 to Ware, where a visual marking or surface discontinuity is placed on the brake chamber pushrod. If the mark is visible when the brakes are applied, then the system is out of adjustment. Another example is provided in U.S. Pat. No. 6,411,206 to Weant et al., wherein an electronic stroke monitor system makes use of hall effect sensors to monitor a magnetic field to determine stroke. A sleeve is put around the base of the pushrod, and the signal is transmitted via radio frequencies. Another example is provided in U.S. Pat. No. 5,762,165 to Crewson, where an indicator is mounted to the slack adjuster and chamber clevis and visually shows the amount of stroke that has taken place when the brake is applied. Another example is provided is U.S. Pat. No. 5,913,385 to Thibodeau, where a bracket that is mounted to the chamber stud provides a stationary reference viewing envelope for a visual pin attached to the chamber pushrod or clevis. If the pin is within the reference envelope when the brake is applied, the system is operating within acceptable limits. Another example is provided in U.S. Pat. No. 6,135,242 to Hockley, which discloses a device similar to the Thibodeau '385 patent, but contains a lubricated clevis pin. Another example is provided in U.S. Pat. No. 6,019,197 to Judson, where a grommet is attached to the pushrod and seals the housing when the chamber is at zero stroke. The grommet is also a visual indicator of the system being out of adjustment when the brakes are applied and the grommet has traveled beyond the visual reference.
There are several problems and/or difficulties with the prior art devices and systems illustrated in the above patents. One is that the reference location is often in an obscure location underneath the vehicle making it difficult for the inspector to see if the system is operating within tolerance. In addition, several of the devices and systems of the above patents require the user to be at a certain viewing angle so that a true measurement is observed.
Furthermore, the prior art indicators and reference brackets are often exposed to the environment and in snowy or muddy climates when road slush or grime is kicked up. As a result, the stationary brackets serve as a collecting spot for ice and other debris. This can then obscure the inspector's view or even bend the bracket such that false readings are provided. Such environmental buildup may also damage other parts of the indication system.
A need exists for a brake chamber stroke indicator system and method that addresses the above issues.